Study On Microstructure And Wear Resistance Of H13 Gradient Coating Sprayed By Supersonic Flame

As a commonly used hot die material,no effective way was found to elongate the service life of H13 steel.Thus,in this paper to find a spraying technique and material for the surface strengthening and repairing,in order to improve the hardness and wear resistence of die surface,the High Velocity Oxygen Fuel spray process was employed to fabricate 85%H13/15%Ni-WC?1#coating?,75%H13/25%Ni-WC?2#coating?and a gradient coating of both on the surface of H13.The microstructures,phase structures and interface adhesion mechanism of all the powders and coatings were analyzed and the surface finish,microhardness and shear bond strength of the coatings were considered.Also a test on thermal fatigue property and high temperature friction and wear behavior on the coatings was conducted.It was founded that the microstructure of three obtained coatings is evenly distributed and cohesively bound layer by layer.Each coating and the base are mechanically combined;The main phases of 1#and 2#coating and gradient coating are?-Fe,Cr and WC,which are basically consistent with the XRD patterns of the powders before sprayed.The additional coating phase is Mo₂C,but the peak intensity is small.Although Mo is stable at room temperature,it tends to react with carbon,hydrocarbons,or carbon monoxide to generate Mo₂C at temperatures above 800°C.Therefore,during the spraying process,a small amount of Mo₂C was generated under the conditions of supersonic flame flow heating.The results show that 2#coating exhibits the highest surface microhardness,followed by gradient coating and 1#coating comes third,but they both are higher than that of H13 steel.While microhardness of gradient coating is more uniform than that of 2#coating;At room temperature and the temperature of 600°C,shear bond strength between gradient coating and the base is obviously better than those of 1#coating and 2#coating,so is the thermal fatigue performance at the temperature of 600°C.In friction and wear behavior experiment at the temperature of 600°C,the average wear depth of the substrate is 20.8?m,the average wear depth of the 1#coating is 20.7?m,and the average wear depth of the 2#coating and the gradient coating is respectively 12.5?m and 9?m,respectively.There is no much difference in the wearing depth between 1#coating and H13,The wear depth of gradient coating is significantly less than those of the substrate and the other two coatings,gradient coating high temperature wear resistance is significantly better than H13 steel substrate,When reaching the temperature of 600°C,the wear depth of H13 is as twice as much in gradient coating.